The present invention relates to a control device of an electric vehicle and, particularly, to an elimination of an induction problem of a signal system for such electric vehicle due to high frequency current flowing from such control device through a power transmission line.
FIG. 3 shows a typical example of a conventional control device of an electric vehicle which is disclosed in "Drive/Control Device for Prototype Electric Vehicle for Tokyo Metroplitan Traffic Agency Line No. 12", "Reports in the 23rd Domestic Symposium on Utilization of Cybernetics in Rail Way", pages 236 to 240, Japan Rail Way Cybernetics Conference. In FIG. 3, a d.c. electric power is collected from a power line through a current collector 1, a main fuse 2, a main switch 3, a line breaker 4, a trip resistor 5, a high speed breaker 6, a limiting/charging resistor 7, a charging contactor 8, a line breaker 9, filter reactors 10 and 11, an overvoltage series resister 12, an overvoltage thyristor 13, a resistor 14 and a D.C. potential transformer (DCPT) 15 connected in series with the resistor 14. A filter capacitor 16 of a U-phase inverter 17a constitutes, together with the filter reactors 10 and 11, a reverse L-type filter circuit. The U-phase inverter includes a pair of series connected thyristors each having a parallel diode. V and W phase inverters 17b and 17c are also provided to actuate induction motors 18a to 18d.
When the control device constructed as above is operated as a PWM inverter, a high frequency component having frequency 6 times the inverter frequency is superimposed on a d.c. input due to the pulse width modulation.
Therefore, when it is operated at an inverter frequency f.sub.1 =f.sub.0 /6 where f.sub.0 is an operating frequency of a signal device, a high frequency current having a frequency f.sub.0 flows through the power line which may cause the signal device to malfunction. In order to solve this problem, it has been usual to increase a value of the filter reactors 10 and 11 to thereby reduce the high frequency current to be sent through the power line.
That is, where a voltage level of the high frequency current flowing through the power line and inductances of the filter reactors 10 and 11 are represented by E, L.sub.0 and L.sub.1, respectively, an impedance of the power line when viewed from the inverters 17a, 17b and 17c becomes j.omega.(L.sub.0 +L.sub.1) and, therefore, the high frequency current I flowing into the power line becomes as follows: EQU I=E/j.omega.(L.sub.0 +L.sub.1) (1)
Thus, by increasing the inductance value (L.sub.0 +L.sub.1) of the filter reactors, the current I can be reduced below a predetermined standard of disturbing current for signal device at a predetermined frequency as shown by the equation (1).
In the conventional control device for an electric car, in order to increase the inductance value of the reactors, the size thereof becomes very large, necessarily, which requires a large space for equipping them.